Broad band frequency responsive means



2 Sheets-Sheet l E. R. STOEKLE BROAD BAND FREQUENCY RESPONSIVE MEANS Filed Aug. 19 1929 Feb. 14, 1933.

Feb. 14, 1933. E; R, STOEKLE 1,897,082

BROAD BAND FREQUENCY RESPONSIVE MEANS Filed Aug. 19, 1929 2 sheets-shea 2 E315: ja

Patented Feb. 14, 1933` PAT ERWIN R. STOEKLE, OF MILWAUKEE, WISCONSIN, ASSIG-NOR TO CENTRAL RADIO LABORATORIES, OF MILWAUKEE, WISCONSIN, A CORPORATION OF WISCONSIN BROAD BAND FREQUENCY RESPONSIVE MEANS Application.V filed `August 19, 1929.

This invention relates to electrical circuits and more particularly to means broadly tuned to a band of frequencies adapted for use in radio circuits and amplifying systems.

Heretofore, in the art several known radio receiving systems have employed one or more sharply tuneable circuits which provide the necessary selectivity in combination with series of so-called untuned cascade vacuum tube amplifiers connected to the tuneable circuit or circuits to provide the necessary amplification. Other known forms of radio receiving systems employ a so-called untuned antenna coil and subsequent stages of cascade amplifiers having tuned input circuits. rlhese so-called untuned amplifiers are really tuned to a definite frequency, the electrical impedance factors of the circuit being fixed; and the so-called untuned antenna coils are really coils tuned with the antenna inductance and capacity to resonance with a certain frequency or band of frequencies.

Itis therefore common to iind radio receiving sets operating eiiiciently near one frequency or over a narrow band of frequencies but less eiciently over other portions of the broadcast range. Heretofore in the art it has been customary to broaden the frequency response of such units, the impedance characteristic of which are not manually variable, by introducing into the circuit resistance or damping factors in the form of iron cores. lVhile the use of such means results in the desired broadening of the response, it also produces the undesirable effect of reducing the amplitude of the incoming waves.

An object of the present invention is to broaden the response of such amplifiers or antenna coils as those mentioned above so that they may be eliiciently operated over a wide baud of frequencies while the losses which reduce the amplitude of the electrical waves passing' therethrough are maintained low.

Another object is to provide a novel combination of a coupling unit and vacuum tube which will be more eiiicient over a broad band of frequencies thanthose heretofore devised.

In carrying out these and other objects a Serial No. 386,760.

circuit is so constituted as to have self inductanoe and distriouted capacity combined and related in such a novel manner as to make a circuit substantially resonant to a wide band of frequencies. In one embodiment of such a circuit an induction coil is incorporated therein. A condenser plate and dielectric material are so associated with the coil as to provide cvapacity between the coil and the plate, the coil thus acting as one plate of the condenser. The plate is connected to one end of the coil so that the result is somewhat the same as though a condenser were placed in parallel with a portion of the coil and in series wi 1h another portion. Such a coil unit will be broadly tuned for the reasons eX- plained hereinafter and may be advantageously employed as a coupling between the stages of an amplifier, in the antenna circuit of a radio system having tuned stages of amplilication or in other circuits or systems where a broadly responsive coupling. is desired.

Other objects and advantages reside in certain novel features of the construction, arrangement and combination of parts which will be hereinafter more fully described and particularly pointed out in the appended claims, reference being had to the accompanying drawings forming a part of this specification, and in Which:

Figure l is a cross-sectional view of aradio frequency coil embodyinoY one form of the present invention with a diagrammatic showing of an associated vacuum tube circuit;

Figure 2 is a cross-sectional view of the coil of Figure l, the View being taken on the line 2 2 of Figure l;

Figure 8 is a cross-sectional view of another and preferred form of radio frequency coil with a diagram showing the associated vacuum tube circuit;

Figure 4 is a cross-sectional View of another form of radio frequency coil and a diagrammatic showing of an associated amplitier circuit the coil being adapted for use primarily as a coupling between the stages of a radio frequency amplifier;

l Figure 5 is a cross-sectional View of a furo 3 so as to measure the thereofyand Figure 10 is a chart illustrating the .prini.'

ther Vmodified form `of radio i frequency coilA and a diagram of the associatedfcircuit; Y

Figure 6 is a diagrammatic showing of an antenna circuit With a cross-sectional view the coil being adapted to'broadly tune thel input circuitV of an .audio frequency ampli-` lier;V

Figure 9 is a test apparatus connected to the coil of Figure ciples of theV presentinvention, one-oftA the curve thereon being plotted from readingstaken on testing apparatus likethat offFig-H;

`Referring to Figures l-and`2 of the draw- -ings which illustrate the invention in its simplest form, reference nuineral`v 1 indicates -a suitable cylindrical insulating core Vor, -base for supportinga coil and condenser gplates.

The condenser plates, shown as ,two in num- Y .z i

bereare made of conducting-material suchas tin foil andare positioned on oppositesides of a single layer coil 5. l vlin building this Y unit, a'conducting layer oriplate 2'is mounted directly upon the rinsulating coreV 1,' the plate being. formed into cylinder to vconform With the lshape of the' core and being split longi` tudinally as shown at 3, Figure 2, to prevent the. circulation of eddy currents therein.

Around the cylindrical layer 2,an insulating coating i is provided; i This coatingservesas abinder for the layer 2, and' as a core' for-the kspiral Winding of thecoil 5. The coil 5 is -thenfivound and is Ycovered with a second insulating coating@'Whichfsupports a second and outer lcylindrical conducting layer 7 which is shaped like theminner `layer 2 and correspondingly split as shown at 3 of Fig. 2

to prevent .the circulation of eddy currents` therein.v @The conducting layersr2 and 7Qare then connected together and to the upper end of the coil 5 by means of a conductor suoli as that shown at 8. `fis shown inthisiFvigure the conductor?) is `also connected to thei antenna and to the grid of theivacuum tube 9 While the lower end of the coil 5 is connected tothe ground and to the fila-'ment of them@ i2 and 7 and the coil 5 will decrease in accorda-Iie With the `Well'lznoivn laws expressed by theformulaey i Y l uum tube, thusplacing the combined coil and condenser-unit in therantenna-ground circuit in parallel with the vacuum tube. y It will be noted that the lower end ofthe conducting cylinders 2 and 7Karenot electri` callyconnected to anything( These cylindersserve as one plate of al` condenser, hovv- 'ever, the other plate'of thec'ondenser being the coil 5 0r a portion thereof@l Theinsulating coatings 4'and 6l serveasfthe dielectric v renderthe vacuu diagrammatic vview` showing electrical,- properties e of this condenser. Since the antenna circuit thus has both inductance `(the'coil 5) andV capacityA V(the coil 5 and plates 2 and 7) therein it Willbe evident that it istuned for resonance with a certain frequency or band of frequencies and that When an electroniotive force of a Vresonant frequency'is impressed thereon, the tuning of the coil is such as to manner. v

Thek present constructiondiiers from anA ordinary circuit having inductance and capacity, however, and is such as to'render the antenna circuit responsive to a broad band of frequencies; Thetheoretical operation of the system ofFigure 1 in accomplishing'this "result Willnow befexplained. i

In 'an ordinary circuit,- as for-example one havinrr an inductance coil and a condenser iny b I .L iparallel the inductanceV and capacity' are tube operative in the usual usually'regarded as fixed values so that theoretioallyv at least `there is" only one frequency to 'which theV circuit is timed for resonance. 'llheiconditions fory resonance may beeX- pressed bythe Wellknoivnl formulae .v

,fihfy'vhich' the frequency of the impressed electromotive force. L is the inductance of the circuitfand C thev capacity.' 1n the system of Figure 1, however, because of thepeculiar manner in which the condenser'plates 2and 7 areas'sociated vvith the coilV 5 and the manner in which the coil and plates are connected to theantenna and. ground, both the induc- 1 tancerLrand capacity@ ofthe'circuit vary inversely With a' changing; frequency and the fconditions'for resonance exist overa Wide 'band'.of frequencies. -V j Y vAssuming an eleotromotive force of reso- 'nantjfrequency is impressed between the an- Atenna and ground of Figure 1, currentwill flowtlirough two parallelpaths, onebeing ank 'inductive path through the coil 5 per se and the other being'aninductive and a capacitive path-through a portion of the coil 5 andthe plates 2Y and 7. In the y second pathnien-j ytio`ned,a portion of the coill acts like one plate of an ordinary condenser.

' 115 If .the frequency vof fthe impressedr elec-V troinotivey force'is increased the inductive freactfanceXi'A ofthe coil'will increase andthe 4capacitive react-ance X'Cbetvveen 'the plates v' Xfaaund Xceg@ in'vvhich fL and C representthegfrequency,infV

actance decreases, due to an increase in frequency, more current will flow through the second path mentioned above (that is, the path which contains the capacitive reactance) and less through the first mentioned path. An increase in frequency will lessen the effective number of turns in the coil or the current does not penetrate the coil as far as it r under natural resonant frequency. rlChis results in decrease in the inductance of the coil. rllhe effective area of the coil (that is, the area capable of sustaining a charge of opposite polarity to that on the plates 2 and 7) is also reduced so that a decrease in capacity between the coil and the plates 2 and 7 also results since the difference in potential between the coil and the plates 2 and 7 is distributed over smaller area of the coil. Thus an increase in frequency causes a decrease in both inductance and capacity so that the conditions for resonance as expressed by 'the formulae still hold so that a broadenof the response of the circuit is effected, whereas an ordinary circuit in which the inductance and capacity are not mutually affected by each other to any considerable extent is detuned upon an increase in frequency.

Similarly if the frequency of the impressed electromotive force is decreased, the inductive reactance decreases and the capacitive reactance increases, resulting in an increase in both the indue-tance and capacity so that Uhe conditions for resonance still hold. It will thus be seen that the condenser and the coil mutually modify the action of each other so that the action of one is controlled not only by conditions in the circuit but also by conditions in the other. In other words, with increased or high frequencies of the broadcast range, the entire coil does not have opportunity to function as an inductance nor does the entire condenser have opportunity to function as a capacity because the current is shunted through a. small part of the condenser after it has penetrated only a few `rns of the coil. As a consequence, with an crease in frequency a decrease in the eifecve or functioning inductance and capacity f the circuit results. Conversely when the requency decreases, more turns of the coil ."ill e penetrated due to the decrease in the inductive reactance and a greater portion of the condenser will function orbe effective. It is to be noted that this broadening in tunof the coil unit is not accompanied by an increase in resistance or by the introduction of other losses.

Referring now to Figure 3 which shows a preferred form of construction a cylindrical insulating tube or core 10 is provided for supporting a pair of insulated coils. The Coil 11 is first wound upon the core and is then coated with an insulating layer 12 upon which the second coil 13 is wound as shown. The

4 Pho WH C i.

l direction of winding of the coils 11 and 13 is important and is such that if the coils Were connected in parallel by connecting the upper ends to the antenna and the lower ends to the ground, the magnetic fluxes generated by the passage of current therethrough will be in opposition. In actual practice the coils are not connected in parallel, however, the lower end of the coil 13 being free and not electrically connected to anything. The upper ends of the coils 11 and 13 are connected to each other kby a conductor 1a' which also connects the upper ends to the antenna and to the grid of a vacuum tube 9 while the lower end of the coil 11 is connected to the lilament of the vacuum tube and to the ground so as to place the coil unit in parallel with the input circuit of the tube.

In this structure it will be seen that the second Winding 13 takes the place of the condenser plates 2 and 7 of the embodiment of Figure 1 being separated from the coil 11 by the dielectric 12. rlhe coil 13 acts to give an additional inductance to the circuit, however, in addition to acting as the plate of a condenser. The operation of this unit is the same as that of Figure 1 except for this additional inductance of the coil 13. Due to the fact that the inductive reactance of the turns of both coils 11 and 13 increases with increasing frequency whereas the capacitive reactance between themy decreases with increasing frequency, a progressively lesser number of turns will be edective in the input circuit of the vacuum tube as the frequency increases. Vl`his will result in a decrease of both the inductance and capacity eective in the input circuit as in the embodiment of Figure 1 and for the same theoretical reasons except that the coil 13, being wound in opposition to the coil 11 further broadens the timing. Assuming the frequency increases above natural resonance, the impedance through the circuit of the coil 13 will decrease, since this circuit contains capacitive reactance. More current will thus flow in coil 13 and the opposition to the field built up by current in the coil 11 will be increased. The effective inductance of coil 11 is thus decreased by the combined action of the inductance of the coil 13 and the capacity between the coil 13 and coil 11. Therefore, the tuning of the input circuit of the vacuum tube will tend to adjust itself to the incoming frequency and an increased efficiency of the coupling will result over a broad band of frequency.

Figure t shows a radio frequency transformer embodying the principles of the invention. An insulating tube 15 is provided upon which three windings 16, 17 and 18 are wound, the windings being separated by insulating coatings 19 and 2O similar to that of the construction of Figures 1 and 3. In order to broadly tune this transformer, large capacity between the primary and secondary 'isprovidedg This result is effected by using the winding 17 Vas the primary and thev windings 16 and 18 as-the secondary. The windfwindings 16 and 18 may be connected to the grid and filament of a vacuum tube;24fby means of the conductors 525 and 26. Nhen the windings are so connected, there is large vcapacity between and idistributed along the turns of thev primary and secondary, because the secondaryis on Ybothvsides of the primary coil. "The'large capacity shunts olf a portion of the current and as an increase in frequency of the impressed voltage causes a; decrease in the. penetration or 4effective turns in fthe.

primary as wellasa decrease inthe effective capacity between the primary and secondary, the inductance and capacity in the input circuit'of the vacuum' .tube will automatically tendto adjust the circuit toresonance with the frequency of thevimpressed voltage over .aV relatively wide band. i Y' An 'alternating'-,electromotive force l impressedacross an intermediate winding 17 will penetrate a progressively greater number of turns as the-frequency decreases which will result in more current being induced in the windings 16 .and 18 by the current in the 1n- -termediate winding 17 .and will also cause greaterelectrical capacity between the coils Y 16 and 18 andthe coil 17` thus vthe inputcircuit will tend. to adjust itselfgto resonance with the impressed electromotiveforce over i alrelatively wide bandof frequencies.V o

Figure 5 shows a Aform of broadly tuned coil likethat ofFig'ure 3 in all respects eX-j cept that the two coils 27 and 28 are composedv of a material. in the form offlattened wire or ,ribbon in order to .increase the distributed Vcapacity between them. In this ligure `the icoil 27 is wound directly upon the tubeV 29 and is then covered with anfinsulating coat ing 30 upon which the outer coil 28 is wound.

-The connectionv and operation of this coil is the same as tliatof Figure 3.

Figure 6 shows a further modification/in which' thebroad tuningjis accomplished by' means of a multi-tap condenser unit which is connected to VVa-coil, such as that diagramfits length.'v Thecondenser unit mayconsist V'of a metallic stud or bolt33 upon whichmematically shown at;32 at suitable points along tallic plates for disks 31, 34, 35,36, 37 and 38 .i are mounted, these plates being. electrically connectedto each other and tothe stud. Al-

ternating withand insulated from the above plates are conducting plates 39, 40, 41, 42 and Vlike through -audio frequency 43.' y,These alternatingsets of plates are separated by a suitable dielectric such aslmica sheets 61. Each of the plates 39, 40, 41, 42 and v43 is connected to a section ofthe coil 32 whereas the plates.V 34, 35, 36, 37 and 38 are connected through the `stud 33 to the .grid of the vacuum tube 44, the antenna and the upperk end of the coil 3.2, as shown. VThe small sectionl condensers, asethose formed by adjacent platesy ofthe condenser unit, thus form Vaseries of parallel-circuits with the sections yof the coil 32 in a manner shown in Figure 6` and shown jdiagrammatically in the input circuit of the first vacuum tube 44of Figure 7. Such a vacuum tube input circuit will therefore respond to a broad band of frequencies determined by the natural frequencies of the several sectional parallel circuits and the combination thereof.

v Figure 7 shows-a portion of a radio receiving system up toandinclu-ding the detector tube. -Thevacuum tubes '44, 45 and 46 are radio frequency amplifiers and the vacuum o tube 47. is' the detector.u The inputcircuit of .thetube 44is broadly tuned by means of the V.sectional condenser unit of thetype shown in Figure 6IV asy mentioned above. The input circuits oftubes .45 and 46 are ofthe usual formr being sharply tunable by means of variable condensers 49 andy50uin Vorder to attain selectivity. The input circuit of the detector 47 is broadly timed by means of a. radio frequency transformer of the type shown inF ig- A ,ure 4. ln viewof the fact that the eiiciency ofy the 'conventional'I Vtuned input circuits of tubes 45 yand 46 is greatestat the shorter wave length (approrimatelyV 350 meters) of the broadest range, it is desirable'to make. the

broadly tuned 'input circuits of tubes 44 and 47 y with the resonance peak near the maximum wave lengthsof the broadcast range (approximately 450 meters) .Y This will give Vthe flattest-response vof .the entire amplifier over the i broadcast range of frequencies.

.Y F igure8 illustrates a form ofbroadly tuned 1i l` transformer adapted for audio frequency amp-lification. -Theobject of this arrangement is to transmit with maximum frequency all of thekaudiofrequencies from a detector or the amplifiersto a sound ieproducer or' speaker. l

The same principles of inductance and kdisf tributed capacity,areapplicablein this circuites inthe previously describedradio free quency circuits except that the values of inductance and capacity mustbemuch greater.

In order to accomplishthis a coil wound and constructed similar toVV that of Figure 4may' .be used, except that? more llayers of windings separated by dielectric lsheets are needed and 'the inductance of tlieunit'mustbe increased by some means such as a laminated iron core 51. In illustrating this transformer, five `layers of :windings are shown, thel first -layerV of .windings being insulated from, the iron core by means of an insulating tube 52 and being connected at its lower end to the lower end of the third winding by a conductor .53, the upper end of the third winding being connected to the upper end of the fifth winding bv the conductor 54. rllhe second and fourti layers of windings are insulated from the first, third and fifth windings by dielectric sheets 52 and are connected in series so as to constitute the primary of the transformer while the first, third and fifth windings constitute the secondary thereof. Just as described for radio fsequency currents in connection wit. 'the device of Figure the alternation of the primary and secondary windings causes a large capacity between these elements which is effective to broadly tune the transformer, the inductance and capacity between the lavers of the coils varywith the impressed frequency in such a manner as to inahe the inputcircuit of the f* tcuum tube respond to broadband of audio freoucncies. rl`his tenus to equally amplify all tb ueucies impressed thereon and the i.

icy source 55 through a transformer 56. 'cometer 57 is connected across the onsite to the inductive and capacity couuq between these two coils. lii'determrfng the coupling between these the fariable frequency source 55 so conred may be operated to impress an electromotive force upon the coil l1 over a wave i from approximately 850 to 600 meters.

of a test svsten litre that of Figure 9 upon a coil actual/lv cons lructed in the form shown oure 3 are plotted on the chart of Figil). in which the curved line B illustrates esnonse of 't ie coil as indicated by the vanometer over the frequency range rEhe sharply peaked resonance curve of Figure l shows the response of a` coil having an inductance valve equal to that of the coil l1 and having an air condenser connected in parallel therewith when subiected to the saine varying wave lengths. It is apparent from the inspection of this chart that a` very much broader band of wave lengths is embraced by the curve B than by thek'curve thus illustrating the results desirec in this invention.

hile only few of the embodiments of -e invention have been shown and described it is obvious that b v making suitable s in the inductance and capacity valves coils shown in Figures l, 8, 5 and 6 l v also may be adapted to audio frequency as ivell as the forni shown in Figure d and th many other changes may be made in t1 structure and in the method of connecting the coils to the apparatus with which they are used without departing from the spirit of the invention or the scope of the annexed claims.

What l claim is:

l. In combination with an electrical system, means lfor impressing energy t icrcon including two parallel electrical paths, one inductive and containing1 an induction coil and the other capacitive and including said induction coil and a condenser plate'co-extensive with and closely adjacent said coil, there being a cli-electric between the coil and the condenser plate whereby as the frequency increases the current will flow more and more through the capacitive path and less through the inductive path and as the frequency de- 1 creases the current will flow more and more lirough the inductive path and less through the capacitive path.

2. In combination with an electrical system, means for impressing energy thereon including an electrical circuit, an induction coil having its terminals connected across the circuit, a second coil disposed in capacitive relation to the first coil, said second coil having one end only connected to said circuit, there being a dielectric between said coils so that the two coils constitute the plates of a condenser as well as the inductance in the circuit and Y whereby vthe inductive and capacitive re` actance of the coils automatically varythe extent of the coils effective as inductance and capacity in the circuit inversely with changes in frequency so as to maintain the circuit resonant to a broad band of frequencies.

3. A vacuum tube amplifier of radio frequency signals comprising a series of vacuum tubes, the output circuit of one tube being coupled to the input circuit of the next succeeding tube in the series by means of closely adjacent, coaxial coils placed one within the other and separated by a dielectric to provide a capacitative as well as an inductive coupling between the coils, one of said coils beconductively connected at one point only to the circuit with which it is associated whereby the effective inductance and capacity of said circuit will vary with the frequency in such a manner as to transfer a wave ,of large amplitude to said input circuit over a broad band of frequencies.

e. ln combination, a vacuum tube, an input circuit for the tube including an antenna having an induction coil connected across said circuit, a multitap condenser unit having a set of plates connected to the coil at spaced points therealong, a second set of plates connected to one side of said circuit and a dielectric between adjacent plates of the sets.

5. ln combination, a vacuum tube, an input circuit :lor the tube including an antenna, an induction coil connected to the antenna and to the ground, a second coil arranged concentrically with respect to and in capacitive rela- 6V Y Y Y 11,897,082'

tion tothe lirstcoil and connected to one side' only of the circuit, there being a dielectric between said coils, thereafter whereby to provide a distributed capacitycoupling between said coils.` i

6. vMeans'for broadly tuning an alternating current circuit to render'thesarne substantiaL ly resonantto abroad band ,of frequencies including aplurality Qfjuxtaposed 'inducek 10 tance coils arranged concentrically one "with-1 in the other, both terminals ofone of said coils being connected 'across' the" circuit andthe other of 'sa-idcoils having a free end and an end connected to one end of the coil connected` 115 across the circuit.

'7 i117. An electrical circuit havingfan induc- Y tion kcoil incorporated 'thereinf'aj condenser Y i plate connected toone side .ofv the circuitand Y disposed closely adjacent-the coilysaidcon- 2b denser plate being co-extensive Awilith said *i coil there-being a dielectric between the coil and the condenser plate so that the coil` constitutesthefotherrplateff theV condenser Vas ywelllas lthe'linductance'gin -the circuitand Y whereby the inductivevr and capacitive re# act'ance of the coil Iand theplateauton'iatical- Y 1y 'vary the eXtentof the coilgandV the plate effective as inductance and capacity in `the ciro. vcuit inversely A with c liangesuin frequency sopas tomaintainthecircuit resonant toa-'broad bandof frequencies. i f

' 1 f8.' An electrical circuit having an induction* coil incorporated "therein, rneans rco'acting with the coilto provide va condenser,` one platel 35 of which is subject 4to the electricalconditions Y obtaining in the coil, the other plate of Vwhich o is connected'to apart of the circuit-wherebyv the inductive and capacitive reactances of the coil and condenser vary the nuinberof turns i4@ of the coil and the area of the condenser effective as inductance and capacity in thecircuit inverselyfwith changes in the frequency. f e 9. An electrical circuit having inductive means incorporated therein,k means connected n to a part of the circutandcoacting with-the l' 'inductivepmeans to supply'distributedca-` Y pacity in electrical relation to and co-vextensivewiultheinducnve meaeswherebythein;

ductive and capacitive -reactances are varied Y 56 with changes in the-frequency impressed on Y' the circuit andlcont-rol the extent of the inductive and distributed capacitive ineanseffective in the circuit 'to V'thus 'automatically maintainingthe'circuit in resonance with the frequency impressed thereon." z

VIn witness whereof,r I hereof ',aiiX-my signa@A `ture.-'

'ERwINR. 

